The present invention relates to an electrode to which a lead is connected and a production method thereof, and a battery using the electrode and a production method thereof.
In recent years, along with the recent progress of the electronic technology, there have been developed small-sized portable electronic apparatuses such as camera integrated video tape recorders and portable information terminals. To cope with the tendency to reduce sizes of these portable electronic apparatuses and to enhance performances thereof, there have been strong demands to develop small-sized, lightweight batteries having high performances as portable power sources used for these electronic apparatuses.
In particular, to drive an electronic apparatus requiring a large pulse current, it is important to use a battery having a high discharge load characteristic as a power source of the electronic apparatus. To realize such a battery, an electrolytic solution, an active material, and the like of the battery have been actively studied.
The performance of a battery is also dependent on constituent members, irrelevant to battery reaction, of the battery, for example, an electrode lead, a collector, and a connection portion therebetween. In particular, to improve the discharge load characteristic of a battery, it becomes important to reduce resistances of these constituent members.
For example, a gel-like electrolyte battery using a gel-like electrolyte has an electrode sheet formed by stacking a negative electrode, the gel-like electrolyte, and a positive electrode to each other; an outer case formed by folding one laminated sheet into two, in which the electrode sheet is sealed; a negative electrode lead, one end of which is extracted to the outside of the outer case; and a positive electrode lead, one end of which is extracted to the outside of the outer case.
FIG. 1 shows an electrode configuration of each of a negative electrode and a positive electrode of a related art gel-like electrolyte battery. The electrode includes a collector 50, an active material layer 51 formed on the collector 50, and a lead connecting portion 52 configured as an exposed extension of the collector 50, on which the active material layer 51 is not formed. One end of a lead 53 is connected to the lead connecting portion 52. FIG. 2 shows another electrode configuration of each of a negative electrode and a positive electrode of a related art gel-like electrolyte battery. The electrode includes a stack of a plurality of electrode sheets each having a collector 50, an active material layer 51, and a lead connecting portion 52. The plurality of lead connecting portions 52 are overlapped to each other, and one end of a lead 53 is joined to the overlapped lead connecting portions 52.
As disclosed, for example, in Japanese Patent Laid-open No. Hei 11-233096, the lead 53 can be joined to the lead connecting portion 52 by ultrasonic welding. This is effective to join the lead 53 to the lead connecting portion 52 without occurrence of cutout or breakage due to generation of spark.
In the above-described methods shown in FIGS. 1 and 2, however, if a metal foil used as the collector 50 is thin, the contact state between the lead 53 and the lead connecting portion 52 is not desirable at the joined portion between the lead 53 and the lead connecting portion 52, with a result that the joining strength between the lead 53 and the lead connecting portion 52 becomes insufficient. That is to say, since the mechanical strength of the joined portion between the lead 53 and the lead connecting portion 52 is poor, there may occur a problem that the lead 53 be peeled only by a slight tensile force applied thereto.
Further, if the contact state between the lead 53 and the lead connecting portion 52 is insufficient, the electric resistance therebetween becomes large, whereby the inner resistance of the battery is increased. As a result, there may occur a problem that the discharge load characteristic of the battery is degraded.
In particular, for a so-called stack-type battery in which a battery element is formed not by winding a negative electrode and a positive electrode but by stacking them to each other, to improve the capacity of the battery, it is regarded desirable to make the lead connecting portion 52 irrelevant to battery reaction as small as possible. Accordingly, for the stack-type battery, the contact area between the lead 53 and the lead connecting portion 52 becomes small as compared with the winding type battery, with a result that the above-described problems, that is, the reduction in joining strength and degradation of discharge load characteristic become significant.